The present invention relates generally to filters for use in the filtration of fluids and, more particularly, to a disc-type filter.
Conventional disc-type filters generally include an elongated housing and stacked therein a number of slightly spaced apart discs or filter plates. The stack of plates is positioned in the path of fluid flow between two flow ports in the housing, and each plate typically has at least one central opening, with the individual plate openings in communication with one another and with one of the flow ports of the housing. The fluid being filtered flows between the two ports and passes through the spaces between the plates which provide filter action by trapping particulate matter in the fluid.
As the spaces between the plates become clogged, the flow of fluid through the filter is inhibited and it becomes necessary to clean the filter by reversing the flow of fluid and flushing the trapped matter free of the plates. To facilitate cleaning, some filters have plates which are held together during filtration by a releasable compressive force, with the plates permitted to separate to increase the spacing between the plates during cleaning. The increased spacing allows the fluid to more easily and completely free matter tightly lodged between the plates during filtration. A disc-type filter of this general construction is shown in U.S. Pat. No. 4,123,356, and includes a support tube on which the plates are stacked and by which the stacked plates are held in alignment.
A significant disadvantage of filters of this type is in their inability to provide a uniform and predetermined spacing between the plates when the compressive force is removed and reverse flushing occurs. If adjacent plates do not separate sufficiently the cleaning action will not be complete. Although one embodiment of the filter shown in the aforementioned patent (FIGS. 10 to 12) limits the total movement of each plate permitted during cleaning by use of a tapered center support tube and plates with central openings which are of successively decreased size, it provides no means to insure a uniform and predetermined spacing will actually occur between all plates.
The filter relies upon the axial force exerted on the plates by the flushing fluid impinging on the chamfered plate edges to cause separation of the plates. Of course, if adjacent plates adhere together due to corrosion, the adhesive nature of the lodged matter or for any other reason by more than the upward force exerted by the fluid, the plates will not separate at all. The same result occurs if one of the plates adheres to the center support tube since it will prevent all plates below it from separating. Even if separation occurs between some plates, the force of the fluid flow may not be sufficient to separate the plates to the maximum limit and thorough cleaning may not be achieved.
Similar results will occur if the force of the fluid flow is not uniform about the edges of a plate and the plate becomes misaligned on the support tube while being moved. In such a case the spacing between a pair of adjacent plates will not be uniform at all points around their perimeter, and at some points the plates may not be separated sufficiently to allow proper cleaning. Further, to the extent the filter does facilitate increasing the spacing between the plates during cleaning, the filter requires an otherwise unnecessary and flow restricting tapered support tube, and plates with central opening of successively smaller size and fluid carrying ability. The complexity of the filter parts and its assembly are also distinct disadvantages of this type of filter.
Another embodiment of the filter shown in said patent (FIGS. 7 to 9) utilizes "spring discs" to cause initial separation of adjacent discs or plates; however, as in the other embodiment, no means are provided to insure that all plates will be separated by a uniform and predetermined amount as is necessary for thorough cleaning of the filter. Even if initial separation occurs as a result of the spring action, two or more adjacent plates may not further separate and the cleaning action of the reverse flush is inhibited. Additional disadvantages of this type of filter are the difficulty of its manufacture and of selecting a suitable material for the plates which has sufficient resiliency to function as a spring. Another disadvantage is the unsuitability of this plate design for manufacture out of an inexpensive plastic material.
It will therefore be appreciated that there has been a need for a disc-type filter which insures a uniform and predetermined spacing will occur between adjacent plates during cleaning by reverse flushing. Ideally, such a filter should have plates with enlarged and uniform central openings, and have a design which is simple, inexpensive to manufacture, and easy to assemble. The present invention fulfills this need, and further provides other related advantages.